Robot Arm Joint Stiffness Control for Human Safety
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Solution Overview
Problem
Conventional robot arm control devices are not designed for multiple joint robots and fail to ensure safety when interacting with humans, as they do not account for human movement and do not provide optimal control during contact situations.
Innovation Solution
A control device for multiple joint robot arms that includes an impact position acquisition means and an impact countermeasure motion control means, which detects human movement and adjusts the stiffness of joint portions closer to the base to be lower than other joint portions based on the impact position, allowing for safe and optimal contact motions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the robot arm uses high stiffness for precise motion control, then motion accuracy is improved, but safety during human contact deteriorates
Solution Approach 1:
The patent applies dynamics by making the stiffness of joint portions dynamically adjustable rather than fixed. The control device changes stiffness in real-time based on operational context: high stiffness during normal operation for precision, and low stiffness during human contact for safety. This is achieved through dynamic modification of control parameters in the stiffness control unit.
Solution Approach 2:
The patent changes the physical parameter of stiffness by modifying control parameters in the control device. The stiffness control unit adjusts the stiffness of joint portions by changing control parameters based on detected contact forces and positions, enabling the system to transition between high-precision mode and safety mode.
2Device complexity
If the robot arm uses uniform stiffness across all joint portions, then control simplicity is maintained, but safety during contact at different positions deteriorates
Solution Approach 1:
The patent applies local quality by making different joint portions have different stiffness characteristics. The stiffness control unit independently controls the stiffness of each joint portion based on its position and the detected contact situation. This allows the joint portion closest to the contact point to have lower stiffness while other portions maintain appropriate stiffness for task performance.
3Object-affected harmful factors
If the robot arm detects contact force and reduces restoring force, then safety is improved, but motion accuracy deteriorates
Solution Approach 1:
The patent segments the robot arm into multiple joint portions with independent stiffness control. Instead of uniformly reducing restoring force across the entire arm, the stiffness control unit selectively reduces stiffness only in the joint portion closest to the contact point, while maintaining appropriate stiffness in other portions to preserve motion accuracy for task execution.
Data Source
AI summary
A control device (1) for a robot arm (8) which, if a person approach detection unit (3) detects approach of a person, performs control according to an impact between the robot arm (8) and the person. The control performed according to the impact is performed through an impact countermeasure motion control unit (4) and by setting individual mechanical impedances for respective joint portions of the robot arm (8) based on a movement of the person detected by a human movement detection unit (2).